Crystalline polyacrylonitrile polymers have been produced for many years and are basically utilized in the production of acrylic and modacrylic textile fibers. Polyacrylonitrile polymers have several distinguishing structural features and physical properties including high degree of crystallinity with little amorphous phase; orientable at temperatures of about 100.degree. C.; poor mechanical properties in an unoriented form and non-melting. Notwithstanding low production costs and some desirable properties, polyacrylonitrile polymers have only found limited commercial usages primarily including thin-walled articles prepared directly from solution and exhibiting enhanced mechanical properties after orientation.
Block polymers of an acrylonitrile sequence with another polymer sequence, for example, acrylamide are a two phase structure separated into domains wherein the acrylonitrile domain has like crystalline structure to polyacrylonitrile polymer. Such a block copolymer may be readily formed by the controlled acid hydrolysis of polyacrylonitrile polymer and are highly swellable in water with a swelling capacity dependent on the ratio of both sequences and on the number of separate domains. Generally, such a block copolymer exhibits considerable strength in the swollen state caused by the two phase structure and crystallinity of the acrylonitrile domains. Such block copolymers have been shaped by pressure in the swollen state or from thermo-reversible gels (TRG), such as disclosed in U.S. Pat. Nos. 4,053,442 and 4,173,606, respectively.